Triaxial orthogonal array eddy current tensor probe and method based on liquid metal microfluidic channel

Abstract

This invention discloses a triaxial orthogonal array eddy current tensor probe and method based on liquid metal microchannels, belonging to the field of electromagnetic nondestructive testing technology. It includes an excitation coil and a receiving unit disposed within the excitation coil. The receiving unit employs an array of three-dimensional sensing units, each comprising: a cubic frame; and three coil groups respectively disposed on the X, Y, and Z faces of the cubic frame. The coils disposed on the X, Y, and Z faces of the cubic frame are spatially coupled at the intersection edges of adjacent faces using an interlaced weave structure, causing the equivalent electromagnetic centers of the three coil groups to converge in physical space to the geometric center point of the cubic frame. The probe of this invention has a compact structure and is suitable not only for planar surfaces but also for the inspection of pipes or curved workpieces by adjusting the bottom shape. It features a high signal-to-noise ratio and omnidirectional consistency.

Description

Technical Field

[0001] This invention relates to the field of electromagnetic nondestructive testing technology, and in particular to a triaxial orthogonal array eddy current tensor probe and method based on liquid metal microchannels for detecting surface and near-surface defects of metallic materials using the principle of magnetic gradient full tensor (MGT). Background Technology

[0002] Eddy current testing (ECT) is the mainstream method for detecting surface defects in metallic materials. However, existing eddy current testing methods face four major challenges: Directional sensitivity (blind zone): Traditional point probes or planar coils can typically only detect cracks perpendicular to the direction of the induced current. When the crack direction is parallel to the current flow line, almost no signal response is generated, leading to missed detection.

[0003] Spatial resolution versus consistency contradiction: To acquire three-dimensional magnetic field information for omnidirectional detection, existing technologies attempt to use three-dimensional coils. However, traditional manufacturing processes typically employ layered winding (i.e., first winding the X layer, then the Y layer, and finally the Z layer), which presents the following technical bottlenecks: 1) Inconsistent equivalent radius: Due to the physical thickness of the conductor, the coil wound first is located in the inner layer, and the coil wound later is located in the outer layer, resulting in an order-of-magnitude deviation in the average equivalent area (Seff) of the triaxial coil, which cannot meet the stringent requirements for sensitivity consistency in gradient tensor inversion. 2) Electromagnetic center eccentricity: Layered winding prevents the geometric center of the triaxial coil from coinciding on a sub-millimeter scale. In magnetic gradient full tensor inversion, this extremely small deviation of the physical center will be detected by the gradient operator ( 1) Amplification produces severe "pseudo-gradient noise," causing the tensor matrix to lose its symmetry constraint and making it impossible to accurately quantify the defect depth. 2) Interaxial mutual inductance coupling: Traditional orthogonal winding ignores the electromagnetic field distortion at the conductor intersection, and the resulting mutual inductance crosstalk limits further improvement of the signal-to-noise ratio.

[0004] Lift-off effect: Minor jitter (lift-off variation) during probe scanning generates strong background noise, often masking the signal of tiny cracks. Therefore, it is particularly important to develop a novel probe that can eliminate directional blind spots, has high center consistency, and effectively suppress lift-off noise.

[0005] The physical dimensions of the signal are ambiguous: In actual detection, the coil outputs an induced voltage, while the gradient tensor inversion algorithm is based on the magnetic field strength B. Existing technologies often neglect the frequency response and gain calibration in this physical quantity conversion process, resulting in inversion results that are only qualitative and cannot achieve quantitative in-depth evaluation. Summary of the Invention

[0006] The purpose of this invention is to provide a triaxial orthogonal array eddy current tensor probe and method based on liquid metal microchannels, which solves the problems of directional blind zone, sensitivity to lift-off effect, and large measurement error caused by non-coincidence of geometric centers of traditional three-dimensional coils in existing eddy current detection technology.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A triaxial orthogonal array eddy current tensor probe and method based on liquid metal microchannels are proposed. A three-dimensional sensing unit is constructed using an in-situ interlaced weaving method and a "polymer material microchannel encapsulation of liquid metal" process. The microchannel cross-section is designed as a flat rectangle or an ellipse with a very high aspect ratio, increasing the effective cross-sectional area of ​​the liquid metal without increasing the volume. This compensates for insufficient conductivity. It ensures triaxial orthogonality accuracy, constructs high-precision "vector points," and arranges high-precision three-dimensional sensing units in an N×N matrix array to construct a spatial "differential network." Based on the vector data acquired by the array, a magnetic gradient tensor matrix G containing rotational invariant information (NSS) is completely reconstructed, which can completely eliminate the "blind zone" caused by the crack direction being parallel to the current direction in eddy current detection. The probe and method of this invention can achieve omnidirectional high-sensitivity detection of minute defects on metal surfaces and can quantitatively invert the defect location.

[0008] Specifically, On one hand, the present invention provides a three-dimensional braided sensing unit for an eddy current probe, comprising: A cube skeleton; Three coil groups are respectively set on the X, Y and Z faces of the cube frame; The coils arranged on the X, Y and Z faces of the cube skeleton are spatially coupled by an interlaced weave structure at the junction edges of adjacent faces, so that the equivalent electromagnetic centers of the three coil groups converge in physical space to the geometric center point of the cube skeleton. The interlaced weave structure is as follows: when the coils on any two orthogonal surfaces pass through the same edge region, the coil on one surface acts as the warp line and the coil on the other surface acts as the weft line. The two alternately pass up and down to form a continuous weave without fixed nodes.

[0009] On the other hand, the present invention provides a triaxial orthogonal array eddy current tensor probe based on liquid metal microchannels, including an excitation coil and a receiving unit disposed within the excitation coil, wherein the receiving unit employs the aforementioned... Three-dimensional sensing units arranged in an array, .

[0010] Furthermore, this invention provides a defect detection method using a triaxial orthogonal array eddy current tensor probe based on liquid metal microchannels, comprising the following steps: S1. Convert the magnetic field signal of the receiving unit into a voltage signal, and calculate the original magnetic field of the receiving unit based on the voltage signal. ; S2. Calculate the magnetic field gradient tensor using the finite difference method. The horizontal gradient component in; S3. Reconstructing the vertical gradient components based on physical constraints of Maxwell's equations; S4. Perform eigenvalue decomposition on the horizontal and vertical gradient components, and calculate the normalized source intensity to generate a defect image.

[0011] Compared with the prior art, the present invention has the following beneficial effects: This invention achieves physical benchmark accuracy for magnetic gradient tensor measurement: existing orthogonal coils can only detect the presence or absence of a signal, while the weaving process of this invention eliminates the asymmetric error of the tensor matrix from its physical source by ensuring the spatial consistency of the triaxial electromagnetic centers. This is the only physical prerequisite for achieving rotational invariance of normalized source strength (NSS), enabling the probe to perform quantitative inversion at the centimeter depth for microcracks, rather than simply qualitative detection.

[0012] This invention boasts extremely high geometric accuracy and signal-to-noise ratio: Its innovative "in-situ interlaced weaving" process physically guarantees the electromagnetic center coincidence of the X / Y / Z triaxial coils (with errors controllable at the micrometer level), eliminating the asymmetric error of the magnetic gradient tensor matrix at its physical source. This effectively eliminates spurious gradient signals caused by sensor position deviations, significantly improving the accuracy of tensor inversion. This invention naturally suppresses lift-off noise: by employing uniform field excitation combined with gradient measurement, the probe output is essentially a spatial differential signal of the magnetic field. This has a strong suppressive effect on slowly varying background fields and overall lift-off variations (common-mode noise), enabling the probe to detect micron-level cracks even under conditions of rough surfaces or hand-held shaking.

[0013] This invention possesses quantitative depth inversion capability: By combining the tensor Euler deconvolution algorithm, this invention can not only discover defects, but also directly calculate the burial depth of defects, achieving a leap from "qualitative discovery" to "quantitative assessment".

[0014] The absolute coincidence of the electromagnetic centers in this invention: By eliminating the mechanical tension tolerance caused by bending physical conductors, the X, Y, and Z axis flow channels are perfectly topologically interwoven during the design phase (like a spatially woven pipeline). After the liquid metal is formed, its inductance and resistance are highly consistent, completely eliminating the gain gradient error caused by the "small inner circle and large outer circle," thus meeting the stringent hardware requirements of the divergence-free constraints of Maxwell's equations. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the overall structure of Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the overall structure of the three-dimensional sensing unit in Embodiment 2 of the present invention; Figure 3 This is a flowchart illustrating Embodiment 3 of the present invention. Detailed Implementation

[0016] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0017] Example 1: Please see Figure 1 A three-dimensional braided sensing unit for eddy current probes, comprising: A cubic skeleton with a side length of 3mm, the cubic skeleton being a hollow or solid support frame made of non-magnetic material, with guide grooves or positioning holes on its edges for fixing the path of the coil.

[0018] Three coil groups are distributed on the X, Y, and Z faces of the cube skeleton, respectively.

[0019] The coils arranged on the X, Y and Z faces of the cube skeleton are spatially coupled by an interlaced weave structure at the junction edges of adjacent faces, so that the equivalent electromagnetic centers of the three coil groups converge in physical space to the geometric center point of the cube skeleton. The interlaced weave structure is as follows: when the coils on any two orthogonal surfaces pass through the same edge region, the coil on one surface acts as the warp line and the coil on the other surface acts as the weft line. The two alternately pass up and down to form a continuous weave without fixed nodes.

[0020] Each coil group contains N turns of coil, where N is an integer greater than or equal to 1. The coils are arranged according to... The winding sequence ensures the inductance of the triaxial coil. and resistance The results are highly consistent, and the effective magnetic center deviation is controlled within the micrometer level, laying the physical foundation for subsequent high-precision differential calculations.

[0021] The coil consists of a hollow, sealed conductor and liquid metal poured into the conductor. Addressing the physical limitation that the conductivity of liquid metal is lower than that of traditional copper, this invention designs the coil's cross-section as a "flattened" rectangle with a height-to-width ratio, for example, a rectangular or elliptical interface with a height-to-width ratio greater than 3. This significantly increases the effective conductive cross-sectional area of ​​the liquid metal without increasing the volume of the three-dimensional sensing unit. This compensates for the lower conductivity of liquid metal compared to traditional copper, improving the coil's quality factor and the signal-to-noise ratio. While maintaining a small spatial volume, this increases the cross-sectional area of ​​the wire, effectively reducing circuit resistance, suppressing thermal noise, and ensuring the acquisition of high-fidelity voltage signals.

[0022] Example 2 A triaxial orthogonal array eddy current tensor probe based on liquid metal microchannels includes an excitation coil and a receiving unit disposed within the excitation coil. The receiving unit adopts the method described in Embodiment 1. Three-dimensional sensing units arranged in an array.

[0023] like Figure 2 As shown, each three-dimensional sensing unit is considered as a sensor, and the four sensors are arranged in a... Array arrangement, spacing The spacing has been optimized to meet the requirements. The target depth criteria are designed to balance truncation error and measurement noise. The probe's bottom contact surface is designed as a plane, a concave arc surface, or a contoured curved surface to adapt to the surface inspection of sheet metal, pipes, or complex curved workpieces. The probe provides a stable background field through an external uniform field excitation coil to eliminate phase fluctuations caused by the rotating field. The probe is also equipped with corresponding conditioning circuitry and a data acquisition card (ADC) for data acquisition.

[0024] Example 3 like Figure 3 As shown, a defect detection method based on a triaxial orthogonal array eddy current tensor probe of liquid metal microchannels is described, using the aforementioned probe and including the following steps: S1. Convert the magnetic field signal of the receiving unit into a voltage signal, and calculate the original magnetic field of the receiving unit based on the voltage signal. .

[0025] Specifically, according to Faraday's law of electromagnetic induction, the induced electromotive force of a coil is proportional to the rate of change of the magnetic flux passing through it. In a time-harmonic eddy current field (angular frequency ω), In ), passing through the first axis( ) Magnetic flux of the receiving coil The generated induced electromotive force for: ; In the formula, For the first The shaft includes the number of coil turns; For the first Effective cross-sectional area of ​​the shaft.

[0026] Assume the magnetic field strength is sinusoidal: ; Then the coil output voltage The complex form is: ; In the formula, The imaginary unit; The excitation angular frequency; the voltage signal output by the coil is amplified and filtered by subsequent conditioning circuits. Considering the circuit gain, the final voltage signal value read by the data acquisition card (ADC) is: ; In the formula, This represents the complex gain of the conditioning circuit.

[0027] In order to measure the voltage Accurately reverse the magnetic field The comprehensive sensitivity constant is defined in this invention as: ; Therefore, the voltage signal and the original magnetic field The relationship is: ; The comprehensive sensitivity constant It is a complex constant that contains information about phase lag and amplitude gain. In practice, this constant is obtained by calibrating the probe in a known standard uniform magnetic field generated by a Helmholtz coil, thereby eliminating uncertainties in coil manufacturing tolerances (N, S) and circuit parameters (A).

[0028] After completing the physical quantity conversion of S1, the non-orthogonality between the three-dimensional sensing units is further corrected, and a calibration model is applied before measurement: ; In the formula, The magnetic field value calculated in step S1; for The calibration matrix is ​​obtained by rotating the probe in a uniform field and minimizing the gradient residual. get.

[0029] S2. Calculate the magnetic field gradient tensor using the finite difference method. The horizontal gradient component in.

[0030] Specifically, with and For example: ; ; Similarly, it can be calculated and To reduce noise, take .

[0031] In the formula, This represents the array baseline length.

[0032] Magnetic gradient tensor Defined as magnetic induction intensity Spatial derivative matrix: .

[0033] S3. Reconstruct the vertical gradient components based on the physical constraints of Maxwell's equations.

[0034] Because the probe is planar, it cannot directly measure the difference in the z-direction; that is, it cannot directly measure the vertical gradient component by reconstructing the horizontal gradient component. Therefore, this invention performs full tensor mathematical reconstruction based on the physical constraints of Maxwell's equations, specifically including the following steps: Cross-vertical gradient: Using the irrotation condition ,Right now It can be measured The rate of change of the horizontal level is used to obtain: ; Pure vertical gradient: Using the dispersion-free condition That is, the trace is zero: ; The above formula shows that the rate of change of the magnetic field in the vertical direction can be accurately derived from the "squeeze" or "stretch" rate in the horizontal direction, thus realizing "two-dimensional array measurement of three-dimensional tensors".

[0035] S4. Perform eigenvalue decomposition on the horizontal and vertical gradient components, and calculate the normalized source intensity to generate a defect image.

[0036] To eliminate the influence of crack orientation on detection sensitivity, this invention uses normalized source intensity (NSS) imaging to calculate the tensor matrix. eigenvalues ( )Build NSS metrics: ; In the formula, Tensor matrix eigenvalues.

[0037] The NSS scalar field exhibits an isotropic single-peak response directly above the crack, completely eliminating the blind zone of traditional eddy current probes.

[0038] To quantitatively assess defect depth, a method was invented to invert defect depth using the tensor Euler equation (Euler deconvolution):

[0039] in The coordinates of the measuring point are... The structural index of defects. The background magnetic field. The tensor Euler deconvolution equation is also often expanded as: ; Solving this overdetermined system of equations within a sliding window will directly yield the coordinates of the defect center. For microcracks, the structural index The value range is usually set as follows .

[0040] Although the above embodiments are based on planar arrays, the principles of this invention are equally applicable to curved surface detection. By arranging the three-dimensional sensing units on an arc-shaped base with the same curvature as the pipe being measured, and introducing a curvature correction factor to the baseline in the difference formula... With modifications, this invention can be used for the inspection of the inner / outer walls of oil drill pipes or pipelines.

Claims

1. A three-dimensional braided sensing unit for eddy current probes, characterized in that, include: A cube skeleton; Three coil groups are respectively set on the X, Y and Z faces of the cube frame; The coils arranged on the X, Y and Z faces of the cube skeleton are spatially coupled by an interlaced weave structure at the junction edges of adjacent faces, so that the equivalent electromagnetic centers of the three coil groups converge in physical space to the geometric center point of the cube skeleton. The interlaced weave structure is as follows: when the coils on any two orthogonal surfaces pass through the same edge region, the coil on one surface acts as the warp line and the coil on the other surface acts as the weft line. The two alternately pass up and down to form a continuous weave without fixed nodes.

2. The three-dimensional braided sensing unit for an eddy current probe according to claim 1, characterized in that, Each of the coil groups contains N turns of coil, where N is an integer greater than or equal to 1; The coil consists of a hollow, sealed wire and liquid metal poured into the wire.

3. A three-dimensional braided sensing unit for an eddy current probe according to claim 2, characterized in that, The cross-section of the coil is a rectangle or ellipse with an aspect ratio greater than 3.

4. A three-dimensional braided sensing unit for an eddy current probe according to claim 2, characterized in that, The cubic skeleton is a hollow or solid support frame made of non-magnetic material, with guide grooves or positioning holes on its edges to fix the path of the coil.

5. A triaxial orthogonal array eddy current tensor probe based on liquid metal microchannels, comprising an excitation coil and a receiving unit disposed within the excitation coil, characterized in that, The receiving unit adopts any one of claims 1-4. A three-dimensional sensing unit arranged in an array, .

6. A defect detection method for a triaxial orthogonal array eddy current tensor probe based on liquid metal microchannels, using the probe described in claim 5, characterized in that, Includes the following steps: S1. Convert the magnetic field signal of the receiving unit into a voltage signal, and calculate the original magnetic field of the receiving unit based on the voltage signal. ; S2. Calculate the magnetic field gradient tensor using the finite difference method. The horizontal gradient component in; S3. Reconstructing the vertical gradient components based on physical constraints of Maxwell's equations; S4. Perform eigenvalue decomposition on the horizontal and vertical gradient components, and calculate the normalized source intensity to generate a defect image.

7. The defect detection method of a triaxial orthogonal array eddy current tensor probe based on liquid metal microchannels according to claim 6, characterized in that, The original magnetic field of the receiving unit is calculated based on the comprehensive sensitivity constant and voltage signal. The expression is: ； in, ； In the formula, The voltage signal acquired by the receiving unit; The excitation angular frequency; This is the overall sensitivity constant; The imaginary unit, For the first The shaft includes the number of coil turns; For the first Effective cross-sectional area of ​​the shaft.

8. The defect detection method of a triaxial orthogonal array eddy current tensor probe based on liquid metal microchannels according to claim 6, characterized in that, The physical constraints of Maxwell's equations include the irrotation condition and the divergence-free condition. Using the irrotation condition By measurement The horizontal rate of change is used to obtain the cross-vertical gradient; Using the dispersion-free condition Obtain the pure vertical gradient.

9. A defect detection method for a triaxial orthogonal array eddy current tensor probe based on liquid metal microchannels according to claim 6, characterized in that, The spatial location of the defect is inverted using the tensor Euler deconvolution equation.

10. A defect detection method for a triaxial orthogonal array eddy current tensor probe based on liquid metal microchannels according to claim 6, characterized in that, After completing the physical quantity conversion of S1, the non-orthogonality between sensors is corrected by applying a calibration model before measurement: ； In the formula, The magnetic field value calculated in step S1; for The calibration matrix is ​​obtained by rotating the probe in a uniform field and minimizing the gradient residual. get.

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